1. Field of the Invention
The present invention relates to a hermetically sealed structure for a junction of two waveguides, e.g., a feeder waveguide and an antenna waveguide, in a microwave circuit.
2. Description of the Prior Art
Conventional hermetically sealed structures for a junction of two circular waveguides will be described below with reference to FIGS. 1(a), 1(b) and 2(a), 2(b) of the accompanying drawings.
FIG. 1(a) and FIG. 2(a) are transverse cross-sectional views and FIG. 1(b) and FIG. 2(b) are fragmentary longitudinal cross sectional views.
FIGS. 1(a) and 1(b) show a conventional hermetically sealed structure for a junction of two circular waveguides. As shown in FIGS. 1(a) and 1(b), a circular waveguide 1 has an end coupled to an end of another circular waveguide 2 by a junction having a disk-shaped hermetic seal 3 sandwiched between the coupled ends of the circular waveguides 1, 2. The junction also includes an annular gasket 4 placed in an annular groove which is defined in the end of the circular waveguide 2, and hermetically held against the hermetic seal 3. The circular waveguide 1 may serve as an antenna waveguide connected to an antenna device, and the circular waveguide 2 as a feeder waveguide connected to a radio transmitter/receiver device.
In order to cancel out a susceptance produced by the hermetic seal 3 and achieve an impedance match at the junction, the circular waveguide 1 has a susceptance correction ring 5 projecting radially inwardly at the joined end thereof near the hermetic seal 3.
FIGS. 2(a) and 2(b) show another conventional hermetically sealed structure for use with a junction between two circular waveguides. Those parts shown in FIGS. 2(a) and 2(b) which are identical to those shown in FIGS. 1(a) and 1(b) are denoted by identical reference numerals. The conventional hermetically sealed structure shown in FIGS. 2(a) and 2(b) differs from the conventional hermetically sealed structure shown in FIGS. 1(a) and 1(b) in that susceptance correction screws 6 are mounted in suitable locations on an inner circumferential wall surface of the circular waveguide 1 near the hermetic seal 3.
The conventional hermetically sealed structure shown in FIGS. 1(a) and 1(b) is complex in structure and expensive to manufacture because of the susceptance correction ring 5 on the circular waveguide 1.
With the conventional hermetically sealed structure shown in FIGS. 2(a) and 2(b), it is necessary to insert and adjust the susceptance correction screws 6 after the circular waveguide 1 is assembled. If the circular waveguides 1, 2 are used outdoors, then the hermetically sealed structure needs to have a certain drip-resistant structure.
Furthermore, if the antenna coupled to the 10 circular waveguide 1 employs two-frequency cross polarization, then since corrective quantities for the respective polarization components are different from each other, the conventional hermetically sealed structures are more complex in structure.